How should human-driven and autonomous vehicles behave at a zebra crossing? Determining acceptable stopping distances and setting-off times.

Autonomous vehicles (AVs) offer a range of substantial safety and mobility benefits. However, successful deployment of AVs will involve interacting with other road users, such as pedestrians and other human-driven vehicles. While previous research has focused on factors that influence perceptions of AVs, less work has addressed how specific interactions with other road users influence acceptability from multiple perspectives. Accordingly, we conducted six studies examining how vehicles, either human-driven or autonomous, should behave at a zebra crossing in terms of stopping distance from the crossing, how long a vehicle should wait before setting off, and the influence of traffic context. Using computer-generated videos we found that: the optimal stopping distance was just before the stop line; participants were generally accepting of a vehicle that waited until a pedestrian had fully cleared the crossing before setting off, and sometime earlier; the presence of other vehicles, context and observer viewpoint can affect judgements of vehicle behaviour; autonomous vehicles were judged more harshly than human drivers with learner drivers judged less harshly in some circumstances, and that vehicle size appeared to have little influence over the acceptability of vehicle behaviours. The results are important for informing the design of autonomous vehicle manoeuvres from the viewpoints of vehicle occupants and other road users.